1. Field of the Invention
The present invention relates to a semiconductor cleaning apparatus for cleaning semiconductor wafers and a wafer cassette for accommodating the semiconductor wafers.
2. Description of the Related Art
The structure of a conventional semiconductor cleaning apparatus is shown in FIG. 90. A product cassette accommodating non-cleaned wafers is injected into a loader/unloader portion 11. The product cassette is, by a conveyance robot (omitted from illustration), moved to a shifting portion 12. In the shifting portion 12, the wafer is shifted from the product cassette to a cleaning cassette. The cleaning cassette accommodating the wafers 1 is held by a cassette hand of a portion 19 for conveying products to be cleaned so that it is sequentially moved to a cleaning portion 14, a water cleaning portion 15 and a drying portion 16. Thus, the process for cleaning the wafers 1 is performed.
FIG. 91 illustrates a cleaning cassette 2 held by the cassette hand of the portion 19 for conveying products to be cleaned. The cleaning cassette 2 is so arranged as to be capable of accommodating a plurality of wafers 1. The cassette hand comprises a chuck-support arm 19b connected to a movable arm 19a and a chuck 19c supported by the foregoing chuck-support arm 19b, the chuck 19c supporting a flange 2a of the cleaning cassette 2 so that the cassette 2 is held by the cassette hand.
The process for cleaning the wafers 1 will now be described with reference to FIG. 92. First, the movable arm 19a is retracted while holding the cassette 2 by making use of the chuck 19c and the movable arm 19a is moved along a rod 19d so that the cassette 2 is positioned above a cleaning chamber 14a of a cleaning portion 14. Then, the movable arm 19a is extended to move the cassette 2 downwards to be immersed in a cleaning solution 14b in the cleaning chamber 14a. Since the upper end of the cassette 2 is, at this time, substantially the same height of the upper end of the wafer 1 accommodated in the cassette 2, complete immersion of the wafer 1 in the cleaning solution 14b causes the chuck 19c to be immersed in the cleaning solution 14b.
The chuck 19c is then opened by the support arm 19b, and then the movable arm 19a is so retracted as to place the chuck 19c on standby at a position above the cleaning portion 14. After the wafer 1 has been processed in the cleaning solution 14b, the movable arm 19a is again extended so that the cassette 2 in the cleaning solution 14b is held to be taken out of the cleaning chamber 14a, followed by immersing the cassette 2 in a water cleaning solution 15b in a water cleaning chamber 15a. During a period in which the wafer 1 is subjected to the water cleaning process in the water cleaning solution 15b, the chuck 19c is on standby at a position above the wafter cleaning chamber 15a. After the water cleaning process has been completed, the chuck 19c is used to take out the cassette 2 in the water cleaning chamber 15a, and then the cassette 2 is set into a drying portion 16. During a period in which the wafer 1 is, together with the cassette 2, subjected to the drying process to be performed in the drying portion 16, the chuck 19c is moved to a hand cleaning portion 13 by the movable arm 19a. In the hand cleaning portion 13, the chuck 19c is cleaned and dried. Then, the chuck 19c is used to hold the cleaning cassette 2 positioned in the drying portion 16 and to be moved to a standby portion 17.
The cleaning cassette 2 accommodating the wafer 1 subjected to the cleaning process is moved from the standby portion 17 to the shifting portion 12 by a cleaning cassette conveyance portion 18. In the shifting portion 12, the wafer 1 is shifted from the cleaning cassette 2 to the product cassette before the wafer 1 is discharged to the loader/unloader portion 11. It should be noted that the product cassette has a structure similar to that of the cleaning cassette 2.
However, a conventional cleaning apparatus of the type arranged as described above is arranged such that the chuck 19c is immersed in the cleaning solution 14b and the water cleaning solution 15b whenever the cleaning cassette 2 is injected and ejected to and from the cleaning chamber 14a and the water cleaning chamber 15a. Therefore, the chuck 19c must be cleaned and dried in the exclusive hand cleaning portion 13 in order to take out the dried wafer 1 and the cassette 2 of the drying portion 16. As an alternative to this, an exclusive conveyance portion having a chuck, which has been previously dried, must be disposed in order to take out the cassette 2 of the drying portion 16. As a result, there arises a problem that the size of the cleaning apparatus cannot be reduced.
Since the portion 19 for conveying products to be cleaned continuously performs the operation for conveying the cleaning cassette 2 accommodating the wafer and the operation for cleaning and drying the cassette hand, the portion 19 for conveying products to be cleaned must perform excessively heavy labor and the time taken to complete the operation becomes too long. Therefore, another problem arises in that the performance of the cleaning apparatus deteriorates.
In the cleaning chamber 14a of the cleaning portion 14, the cleaning solution 14b is heated and the raised temperature is maintained by a heater or the like to perform the process. If light etching is performed, for example, SC1 (NH.sub.4 OH+H.sub.2 O.sub.2 +H.sub.2) is heated to 40.degree. C. to 50.degree. C. and this level is maintained. If the resist is removed, for example, sulfuric acid, water, and peroxide (H.sub.2 SO.sub.4 +H.sub.2 O.sub.2 +H.sub.2 O) is heated to 140.degree. C. to 150.degree. C. and this level is maintained to perform the desired process. Since the semiconductor cleaning apparatus is placed in a clean room, its atmospheric air temperature is controlled to, for example, 25.degree. C. Therefore, the cleaning solution 14b is evaporated from the surface as a chemical mist 14c which is, as shown in FIG. 93, then diffused while wafting on an upflow 14d of a natural convection generated on the surface of the cleaning solution 14b. In order to prevent this, a local exhaust duct 14e is locally disposed above the cleaning chamber 14a so that the chemical mist 14c wafting on the upflow 14d of the natural convection is, together with the exhaust flow, sucked.
On the other hand, the conveyance robot of the conveyance portion 19 is moved vertically while holding the cleaning cassette 2 with the cassette hand thereof to immerse the cleaning cassette 2 in the cleaning solution 14 and ejecting the same from the cleaning solution 14b.
However, the local exhaust duct 14e cannot completely suck the upflow 14d of the natural convection and the chemical mist 14c from the entire upper surface of the cleaning chamber 14a, resulting in that a portion of the chemical mist 14c outwards diffuses. When the cleaning cassette 2 is taken out of the cleaning solution 14b, the cleaning cassette 2, which is wet with the cleaning solution 14b, is raised to an upper position which is not affected by the local exhaust. Therefore, the chemical mist 14c is newly generated in the wet cleaning cassette 2, the chemical mist 14c thus-generated being then diffused. Therefore, the chemical mist 14c adheres the conveyance robot of the conveyance portion in the semiconductor cleaning apparatus. As a result, there arise problems in that the conveyance robot is corroded and that the adhesion of the chemical mist 14c to the product wafer causes defects.
Another problem arises in that the chemical mist 14c wafts on the circulation flow in the clean room and diffuses and, accordingly, the equipment is corroded or the product wafer is defective.